The sloping loads in LAVA are automatically calculated for you.
The Roof Load Assembly allows you to enter a slope, and it will automatically create a Slope Adjustment. This slope will apply to all the plates that use this Roof Load assembly.
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Note: The slope can also be adjusted on individual Plates by opening the Plate dialog. This will change the calculated slope adjustment for this individual plate.
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How is the Slope Adjustment Calculated?
When you review your load assembly and results, you’ll see a line item “Slope Adj” listed.
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Case 1: Flat Roof Joist
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Load Assembly
Tile S 10psf
Sheeting S 1.5psf
Insulation S 1psf
Truss S 2.5psf
Total = 15psf
Case 2: Sloped Roof Joist
Assume a slope of 12 / 12, but the roof joist length remains the same 20’
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Slope adj calculated:
15psf x (20 / 14.14) = 21.21psf
21.21psf - 15psf = 6.21psf, this value matches with LAVA adjustment.
In Case 1, total DL per plf on 20’ span joist is 20’ x 15psf = 300plf
In Case 2, total DL per plf is 14.14’ x 15psf = 212plf without adjustment.
To account for the difference, we can either adjust the DL, or multiply span 14.14’ by 1.414
Since we draw the gravity plate in LAVA based on building dimension, the roof length corresponds to 14.14’ in this case, not 20’, so we adjust the DL instead.
So for a 12 / 12 slope roof, with 15psf input DL, we need to add 6.21psf for a total of 21.21psf DL for gravity design.